Biology of Tooth Movement

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Introduction to Orthodontics
Fifth Year

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Biology of Tooth Movement

  1. 1. 15th Lecture Biology of Tooth Movement-I
  2. 2. Outlines • • • • April 28, 2012 Clinical consideration of the periodontium: Periodontal Ligament: Mechanisms of Orthodontic tooth movement: Tissue Reaction To Tooth Movement: Physiologic Tooth Movement: a) Resorptive bone wall b) Depository bone wall Dr. Ahmed Basyouni 2
  3. 3. Outlines Orthodontic Tooth Movement (OTM): a) Dentoalveolar tissue reaction: i. Pressure side: ii. Tension side: b) Hyalinization April 28, 2012 Dr. Ahmed Basyouni 3
  4. 4. Fact Orthodontic treatment is based on this fact: Orthodontic treatment is possible, by applying appropriate forces to move teeth through the alveolar bone. Accurate and precise control of tooth movement can be achieved with proper use of mechanics and knowledge of subsequent tissue response. April 28, 2012 Dr. Ahmed Basyouni 4
  5. 5. Clinical consideration of the periodontium • Periodontium is a major factor influencing tooth movement during orthodontic treatment. It includes: a) Gingiva b) Alveolar bone c) Periodontal ligament d) Cementum April 28, 2012 Dr. Ahmed Basyouni 5
  6. 6. Periodontal Ligament • Periodontal ligament (PDL) is the connective tissue surrounds the root and attaches it to the alveolar bone. It consists of Cells, fibers, ground substance & normal width 0.5 mm . Functions: 1. Formative 2. Supportive 3. Protective 4. Nutritive 5. Sensory April 28, 2012 Dr. Ahmed Basyouni 6
  7. 7. Mechanisms of Orthodontic tooth movement Modeling and remodeling of the alveolar bone caused by Two basic cellular processes: a) Osteoblastic activity (bone formative) b) Osteoclastic activity (bone resorptive) These two cellular activities remove bone from one place and add it to another, to make characteristic size and shape of each bone for everyone. The DNA encoded information in each cell nucleus or sometimes external (environmental ) could direct cell activities to produce changes in size and shape that occur during growth. April 28, 2012 Dr. Ahmed Basyouni 7
  8. 8. Mechanisms of Orthodontic tooth movement Orthodontic Tooth Movement (OTM) causes: a) Pressure side: cell replication is decreased as a result of vascular constriction. b) Tension side: cell replication is increased, bec. Of stimulation afforded by stretching of the fiber bundles of the PDL. April 28, 2012 Dr. Ahmed Basyouni 8
  9. 9. Periodontal and Other Tissue Reaction To Tooth Movement I. II. Physiologic Tooth Movement: a) Resorptive bone wall b) Depository bone wall Orthodontic Tooth Movement (OTM): a) Dentoalveolar tissue reaction i. Pressure side ii. Tension side b) Hyalinization April 28, 2012 Dr. Ahmed Basyouni 9
  10. 10. Periodontal and Other Tissue Reaction To Tooth Movement I. Physiologic Tooth Movement: Growth of the craniofacial complex in vertical, sagittal and transverse dimensions causes positional changes of the teeth in all three planes of space. a) Resorptive bone wall: Alveolar bone resorption occurs on the side toward which tooth is moving, same time, reconstruction of ligament support between tooth and bone is taking place. April 28, 2012 Dr. Ahmed Basyouni 10
  11. 11. Physiologic Tooth Movement: a) Resorptive bone wall: Microscopically, osteoclasts present in scattered resorptive lacunae on alveolar bone wall. After a while, resorption stop and Howship’s Lacunae will be occupied by other cells depositing new layers of bone to which new periodontal fibrils become embedded. April 28, 2012 Dr. Ahmed Basyouni 11
  12. 12. Physiologic Tooth Movement: b) Depository bone wall: Alveolar bone deposition occurs on the side opposite the direction to which tooth is moving, together with rearrangement of the periodontal fibers. April 28, 2012 Dr. Ahmed Basyouni 12
  13. 13. Periodontal and Other Tissue Reaction To Tooth Movement II. Orthodontic Tooth Movement (OTM): OTM is a biologic response of periodontal tissues to applied forces. Orthodontic forces are much heavier than natural forces responsible for physiologic migration . Histochemical changes and cellular response depend on: 1. Force intensity 2. Force duration 3. Force direction April 28, 2012 Dr. Ahmed Basyouni 13
  14. 14. Periodontal and Other Tissue Reaction To Tooth Movement Orthodontic Tooth Movement (OTM): The ideal force is one which induces a pressure in the periodontal ligament not exceeding the capillary blood pressure i.e. not more than 32 mmHg. April 28, 2012 Dr. Ahmed Basyouni 14
  15. 15. April 28, 2012 Dr. Ahmed Basyouni 15
  16. 16. Periodontal and Other Tissue Reaction To Tooth Movement Orthodontic Tooth Movement (OTM) a) Dentoalveolar tissue reaction: A distinct pressure and tension zone is developed on either side of the tooth after force application. Bone modification is not restricted only to resorption and apposition around tooth in the periodontal space but also, seen in marrow spaces and under periosteum on external surfaces of the alveolar processes. This mechanism shows that, tooth is not simply moved through bone, but supporting structures move with a tooth into a new position as a response to change in its environment. April 28, 2012 Dr. Ahmed Basyouni 16
  17. 17. Periodontal and Other Tissue Reaction To Tooth Movement Orthodontic Tooth Movement (OTM) i. Pressure side: Periodontal cells have differentiated into specialized cells (Osteoclasts) which are responsible for resorption of the alveolar bone wall. In young individuals, resorption process may begin as soon as 12 hours after force application. The periodontal width on pressure side has been initially decreased due to mechanical compression of the periodontal ligament, then greatly increased in order to allow space for high cellular activity and proliferation of vascular structures. April 28, 2012 Dr. Ahmed Basyouni 17
  18. 18. Orthodontic Tooth Movement (OTM) i. Pressure side: A chain of osteoclasts is seen along the alveolar wall. Fibrous supporting apparatus on pressure side is reconstructed by almost complete breakdown of the old fibers and formation of new fibrous elements. The vascular system provides many of the undifferentiated cells that are responsible for reconstructional changes. April 28, 2012 Dr. Ahmed Basyouni 18
  19. 19. Orthodontic Tooth Movement (OTM) i. Pressure side: Effects of LIGHT forces on the periodontium: • Light, continuous forces – Osteoclasts formed – Removing lamina dura – Tooth movement begins – This process is called “FRONTAL RESORPTION”. April 28, 2012 Dr. Ahmed Basyouni 19
  20. 20. Orthodontic Tooth Movement (OTM) i. Pressure side: • “Frontal resorption” because it occurs between the root and the lamina dura. April 28, 2012 Dr. Ahmed Basyouni 20
  21. 21. Orthodontic Tooth Movement (OTM) i. Pressure side: April 28, 2012 Dr. Ahmed Basyouni 21
  22. 22. Periodontal and Other Tissue Reaction To Tooth Movement Orthodontic Tooth Movement (OTM) ii. Tension side: Cellular increase occurs after 30 to 40 hours following application of an orthodontic force. Stretched fibers on tension side is seen to be reconstructed by changes of the original fibrils. New unmineralized osteoid material is laid down around stretched fibers close to alveolar bone wall produced by osteoblasts. Mineralization of the osteoid starts in the deepest layers. April 28, 2012 Dr. Ahmed Basyouni 22
  23. 23. Orthodontic Tooth Movement (OTM) ii. Tension side: April 28, 2012 Dr. Ahmed Basyouni 23
  24. 24. Periodontal and Other Tissue Reaction To Tooth Movement Orthodontic Tooth Movement (OTM) b) Hyalinization Hyalinization occurs when heavy applied forces presses tooth too hard against the alveolar bone wall. Periodontal membrane responds with local degeneration and sterile necrosis. In humans, it takes 1 to 2 days for a hyalinized zone to develop. Tooth is not capable of movement until this hyalinized tissue is removed. April 28, 2012 Dr. Ahmed Basyouni 24
  25. 25. Periodontal and Other Tissue Reaction To Tooth Movement Orthodontic Tooth Movement (OTM) b) Hyalinization Elimination of hyalinized zone occurs by two mechanisms: 1. Resorption of the alveolar bone by osteoclasts. 2. Invasion of cells and blood vessels from periphery of compressed zone by which necrotic tissue is removed. April 28, 2012 Dr. Ahmed Basyouni 25
  26. 26. Orthodontic Tooth Movement (OTM) b) Hyalinization • Effects of HEAVY forces on the periodontium • Heavy, continuous forces cause – Blood supply to PDL occluded – Aseptic necrosis – PDL becomes “hyalinized” – “HYALINIZATION” – This process is called “UNDERMINING RESORPTION”. April 28, 2012 Dr. Ahmed Basyouni 26
  27. 27. Orthodontic Tooth Movement (OTM) b) Hyalinization “Undermining resorption” because it occurs on the underside of lamina dura, not between lamina dura and the root. April 28, 2012 Dr. Ahmed Basyouni 27
  28. 28. FRONTAL RESORPTION Phase 3 Phase 2 Phase 1 Time (Arbitrary Unit) UNDERMINGING RESORPTION Tooth movement (mm) Tooth movement (mm) Orthodontic Tooth Movement (OTM) b) Hyalinization Phase 3 Phase 2 Phase 1 Time (Arbitrary Unit) Frontal resorption facilitates orthodontic tooth movement, whereas undermining resorption impedes orthodontic tooth movement. April 28, 2012 Dr. Ahmed Basyouni 28
  29. 29. Summary • • • • April 28, 2012 Clinical consideration of the periodontium: Periodontal Ligament: Mechanisms of Orthodontic tooth movement: Tissue Reaction To Tooth Movement: Physiologic Tooth Movement: a) Resorptive bone wall b) Depository bone wall Dr. Ahmed Basyouni 29
  30. 30. Summary Orthodontic Tooth Movement (OTM): a) Dentoalveolar tissue reaction: i. Pressure side: ii. Tension side: b) Hyalinization April 28, 2012 Dr. Ahmed Basyouni 30
  31. 31. April 28, 2012 Dr. Ahmed Basyouni 31

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